Soil and/or groundwater remediation process

ABSTRACT

A method of treating contaminants in soil and/or groundwater comprising adding a source of an oxidizing agent and an aqueous solution of a metal catalyst having a pH of from about 5 to 8 to the in situ environment in amounts capable of producing reactive species sufficient to oxidize at least one of the contaminants.

FIELD OF THE INVENTION

[0001] The present invention is directed to methods and systems forconverting contaminants contained in soil and/or groundwater tonon-contaminating or harmless compounds. The methods and systems includetreatment of the contaminants with a source of an oxidizing agent and asubstantially neutral reagent comprising an effective amount of a metalcatalyst to thereby promote and control the conversion of thecontaminants.

BACKGROUND OF THE INVENTION

[0002] The treatment of contaminated soils and groundwater has gainedincreased attention over the past few years because of uncontrolledhazardous waste disposal sites. It is well documented that the mostcommon means of site remediation has been excavation and landfilldisposal. While these procedures remove contaminants, they are extremelycostly and in some cases difficult if not impossible to perform.

[0003] More recently, research has focused on the conversion ofcontaminants contained in soil and groundwater based on the developmentof on-site and in situ treatment technologies. One such treatment hasbeen the incineration of contaminated soils. The disadvantage of thissystem is in the possible formation of harmful by-products includingpolychlorinated dibenzo-p-dioxins (PCDD) and polychlorinateddibenzofurans (PCDF).

[0004] In situ biological soil treatment and groundwater treatment isanother such system that has been reviewed in recent years. So-calledbioremediation systems, however, have limited utility for treating wastecomponents that are biorefractory or toxic to microorganisms.

[0005] Such bioremediation systems were the first to investigate thepractical and efficient injection of hydrogen peroxide into groundwaterand/or soils. These investigations revealed that the overriding issueaffecting the use of hydrogen peroxide in situ was the instability ofthe hydrogen peroxide down gradient from the injection point. Thepresence of minerals and enzymes such as catalase and peroxidase in thesubsurface catalyzed the disproportionation of hydrogen peroxide nearthe injection point, with rapid evolution and loss of molecular oxygen,leading to the investigation of stabilizers as well as biologicalnutrients.

[0006] During the early biological studies from the 1980's, someinvestigators recognized the potential for competing reactions, such asthe direct oxidation of the substrate by hydrogen peroxide. Certainresearchers also hypothesized that an unwanted in situ Fenton's-likereaction under native conditions in the soil was reducing yields ofoxygen through the production of hydroxyl radicals. Such a mechanism ofcontaminant reduction was not unexpected, since Fenton's-type systemshave been used in ex situ systems to treat soil and groundwatercontamination.

[0007] Other investigators concomitantly extended the use ofFenton's-type systems to the remediation of in situ soil systems. Thesestudies attempted to correlate variable parameters such as hydrogenperoxide, iron, phosphate, pH, and temperature with the efficiency ofremediation.

[0008] As with the bioremedial systems, in situ Fenton's systems wereoften limited by instability of the hydrogen peroxide in situ and by thelack of spatial and temporal control in the formation of the oxidizingagent (i.e. hydroxyl radical) from the hydrogen peroxide. In particular,aggressive/violent reactions often occurred at or near the point wherethe source of the oxidizing agent (the hydrogen peroxide) and thecatalyst were injected. As a consequence, a significant amount ofreagents including the source of the oxidizing agent (hydrogen peroxide)was wasted because activity was confined to a very limited area aroundthe injection point. In addition, these in situ Fenton's systems oftenrequired the aggressive adjustment of groundwater pH to acidicconditions, which is not desirable in a minimally invasive treatmentsystem. Finally, such systems also resulted in the mineralization of thesubsurface, resulting in impermeable soil and groundwater phases due tothe deleterious effects of the reagents on the subsurface soils.

[0009] U.S. Pat. No. 5,741,427 describes the complexing of a liganddonor with a metal catalyst to moderate the catalytic turnover rate ofthe metal catalyst. It is indicated that the preferred metal catalystsinclude metal salts, iron oxyhydroxides, iron chelates, manganeseoxyhydroxides and combinations thereof, and the ligand donors generallycomprise acids, salts of acids, and combinations thereof. The describedreaction product complex of the metal catalyst and ligand donormoderates the catalytic turnover rate for a longer time and for afurther distance from the injection point to provide enhanced spatialand temporal control in the formation of the oxidizing agent (i.ehydroxyl radical). Although the system described in the '427 Patentworks well, the reaction product complex is highly acidic with a pH inthe range of 2 to 4, which is undesirable from the standpoint of properenvironmental remediation as well as regulatory review.

[0010] Other researchers have investigated the use of ozone, eitheralone or in combination with hydrogen peroxide, in ex situ advancedoxidation processes (AOPs). These systems suffer from a similarlimitation as the ex situ Fenton's systems; namely, the necessity topump contaminants from the in situ media to an external reaction vessel,a requirement which was both expensive and inefficient. Ozonationprocesses also suffer from low selectivity of contaminant destructionand high instability of the ozone and reactive species generated.

[0011] It would be of significant advantage in the art of removingcontaminants from soil and/or groundwater to provide a system by whichthe source of the oxidizing agent and the metal catalyst can travel fromthe injection point throughout the aerial extent of the contamination inorder to promote efficient destruction of the contaminant plume withoutthe acidification of the subsurface or the resultant mineralization ofthe soils. It would be a further advantage to provide a system by whichthe source of the oxidizing agent is stabilized to allow dispersionthroughout the plume and by which the catalytic turnover rate of themetal catalyst is moderated in order to promote more efficientdestruction of contaminants. It would be of further benefit to providean injection method in which the reagents are injected at the time,concentration, and location most suitable for efficient conversion ofthe contaminants at the specific site. It would be a still furtherbenefit in the art to provide a system which efficiently generates thereactive species, for example hydoxyl radicals, to provide a costefficient and effective method of oxidizing contaminants in soil and/orgroundwater.

SUMMARY OF THE INVENTION

[0012] The present invention is directed to reagents and methods fortreating contaminants in an in situ environment in which an oxidizingagent and a reagent comprising an aqueous solution containing aneffective amount of a metal catalyst having a pH in the range of about 5to 8, is provided to the in situ environment to thereby reduce oreliminate contaminants present therein in a simple, cost efficient andeffective manner without significantly altering or disturbing thenatural features of the environment.

[0013] In accordance with one aspect of the invention, there is provideda method of treating contaminants in an in situ environment comprisingadding a source of an oxidizing agent, preferably a stabilized source ofoxidizing agent, capable of oxidizing at least one of the contaminantsand together or separately with an effective amount of a reagentcomprising an aqueous solution of a metal catalyst having a pH in therange of about 5 to 8 or adjusted to a pH of 5 to 8 with a pH modifyingagent, to the in situ environment to at least reduce the concentrationof at least one contaminant in the in situ environment. Use of thesource of the oxidizing agent and the catalytic reagent enables temporaland spatial control of the oxidation process so that the oxidizing agentis able to be generated into areas where contaminants are present. As aresult, aggressive/violent reactions at the point of injection areminimized and less oxidizing agent is wasted. In addition, due to thegeneration of hydroxyl radicals throughout the plume and the presence ofother reactive species, contaminants normally recalcitrant to otheradvanced oxidation processes are now able to convert to harmlessby-products. The present method is applicable to all areas of the insitu environment especially subsurface areas.

[0014] In accordance with a further aspect of the invention, thestabilized oxidizing agent and the catalytic reagent are injected into aspecific area of the in situ environment known as the capillary fringe.The capillary fringe is that portion of the contamination at a sitewhich lies just above the water table. Destruction of contamination inthe capillary fringe prevents contamination which is often adsorbed inthe capillary fringe from serving as a continuing source of groundwaterand soil contamination.

[0015] In accordance with another aspect of the invention, thestabilized source of the oxidizing agent and the catalytic reagent areinjected into an area of the subsurface environment known as thesaturated unconsolidated zone. The saturated unconsolidated zone is thatportion of the contamination at a site which lies within the watertable. Destruction of contaminants in the saturated unconsolidated zoneprevents contamination which is often adsorbed in the water table fromserving as a continuing source of groundwater and soil contamination.

[0016] In accordance with another aspect of the invention, the methodsand systems herein can be applied to oxidizing contaminants informations which are difficult to access such as fractured bedrock. Inparticular, the source of the oxidizing agent and the catalytic reagentare injected at elevated pressures into the fractured bedrock to treatcontaminants whose density is greater than water and are often trappedin bedrock fractures.

[0017] In further aspect of the invention, the source of the oxidizingagent and the catalytic reagent are injected into an situ environment toenhance the operation and efficiency of traditional remediationtechnologies such as pump and treat and soil vapor extraction systems.The present invention enhances these conventional systems that are basedon mechanical removal of the contaminants. This is because the oxidationreactions which convert the contaminants to harmless compounds alsoenhance desorption of the contaminants from organic carbon in soiland/or groundwater and generally result in enhanced volatilization andreduced adsorption to organic carbon in the soil.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention is generally directed to methods andsystems for removing contaminants from soil and/or groundwater byconverting the same to harmless by-products. Such contaminants typicallyarise from petroleum storage tank spills or from intentional oraccidental discharge of liquid hydrocarbons including, but not limitedto: gasoline, fuel oils, benzene, toluene, ethylbenzene, xylenes, (BTEX)naphthalene, pesticides, herbicides, and other organic compounds;lubricants, chlorinated solvents, including polychorinated biphenyls(PCBs), and pentachlorophenol (PCP); and metals, cyanides, and the like.The list of contaminants provided herein is exemplary. It should beunderstood, however, that other contaminants capable of being oxidizedinto harmless compounds, such as carbon dioxide and water, is within thepurview of the present invention.

[0019] In accordance with the present invention, the methods and systemsfor remediation of a contaminated environment in situ is performed byproviding a reagent comprising an aqueous solution containing aneffective amount of a metal catalyst having a pH in the range of fromabout 5 to 8, and injecting the same along with a stabilized source ofan oxidizing agent, such as a peroxide and preferably hydrogen peroxide,as hereinafter described. The source of the oxidizing agent and thecatalytic reagent reacts in situ to form a reactive species (e.g.hydoxyl radical), as hereinafter described. It has been found that thereactive species generated in this way are found throughout the extentof the plume with a resultant higher efficiency of contaminantdestruction. Neutralizing the pH of the catalytic reagent within therange of from about 5 to 8 moderates the catalytic turnover rate of themetal catalyst.

[0020] In one embodiment of the present invention, the catalytic reagentand the stabilized source of the oxidizing agent are alternatelyinjected (i.e. in cycles) into the soil and/or groundwater. Theprocedure is typically adopted for a subsurface with moderate to highpermeability. In another embodiment of the present invention, thecatalytic reagent and the stabilized source of the oxidizing agent arecontinuously injected into the soil and/or groundwater. This procedureis typically adopted for a subsurface with low to moderate permeability.In a preferred procedure employing cycled or continuous reagentapplication, the catalytic reagent is the first injection in the soiland/or groundwater followed by the stabilized source of the oxidizingagent. In another preferred procedure employing cycled or continuousreagent application, the stabilized source of the oxidizing agent is thefirst injection in the soil and/or groundwater followed by the catalyticreagent. In still another preferred procedure consisting of continuousreagent application, the stabilized source of the oxidizing agent isadded to the in situ environment and allowed to disperse or migratethroughout the plume. Subsequently, the catalytic reagent is injectedinto the in situ environment in at least one injection point through theplume. Applicants have determined that the substantially pH neutralcatalytic reagent provides better dispersion of reagents in thesubsurface and more control over the formation of the oxidizing agent.

[0021] In particular, the present catalytic reagent moderates thecatalytic turnover rate for a longer time and for a further distancefrom the injection point than typical prior art procedures to provideenhanced spatial and temporal control in the formation of the oxidizingagent. The oxidation efficiency of the reagent of the present inventionis therefore superior to prior art systems. Although not wishing to bebound by any theory, it is believed that the pH level of the catalyticreagent promotes a more moderate rate of turnover of the catalyticsystem thereby harnessing its ability to promote the production of theoxidizing agent significant distances away from the injection point.

[0022] The sources of oxidizing agents employed in the present inventionare those that typically generate free radicals (e.g. hydroxyl radicals)and include peroxides such as hydrogen peroxide, calcium peroxide,sodium peroxide, and permanganates such as potassium permanganate andthe like. Calcium peroxide generates hydroxyl radicals under acidicconditions in the presence of iron (II) salts. Calcium peroxide is veryslightly soluble in water and is generally more expensive than hydrogenperoxide. However, calcium peroxide can be used as an effective sourceof oxidizing agent for hydrocarbon-contaminated sites. Sodium peroxidehas been found to behave in a manner similar to calcium peroxide and canbe used as well. Hydrogen peroxide is the preferred peroxide for use inthe present invention.

[0023] Another suitable source of the oxidizing agent is ozone. Ozonehas previously been used as a disinfectant and in more recentapplications to oxidize refractory organic contaminants. Ozone underwell known conditions can generate hydroxyl radicals which is apreferred oxidizing agent.

[0024] The peroxides and ozone, as exemplary hydroxyl radical producingcompounds, can be used alone, in combination with themselves (i.e.ozone-peroxide) or in combination with ultraviolet radiation. What isessential is that the source of the oxidizing agent be capable ofgenerating hydroxyl radicals in sufficient quantity to convert existingcontaminants (e.g. hydrocarbons)to harmless compounds (e.g. carbondioxide and water vapor).

[0025] Prior to injection, the source of the oxidizing agent (e.g.peroxide) is preferably stabilized. Stabilization prevents the immediateconversion of the peroxide via native iron or catalase into hydroxylradicals or oxygen at positions only immediately adjacent to theinjection points. Once stabilized, the peroxide is introduced into thein situ environment, typically in water at a concentration up to about35% by weight. It will be understood that the concentration of peroxidein the in situ environment will significantly decrease as the peroxidespreads out through the soil and/or groundwater. In a preferred form ofinjection into the in situ environment, stabilized peroxide is used at aconcentration less than 10%. Suitable stabilizers include acids andsalts thereof. The most preferred acid is phosphoric acid and the mostpreferred salt is monopotassium phosphate.

[0026] The catalytic reagent employed in the present invention isobtained by mixing an effective amount of the metal catalyst in water atambient temperature to enhance dissolution so that the aqueous solutionof the metal catalyst has a pH of from about 5 to 8. If necessary, theresulting solution may be neutralized with a pH modifying agent to a pHwithin the range of from about 5 to 8. Suitable catalysts include metalsalts, iron oxyhydroxides, iron chelates, manganese oxyhydroxides andcombinations thereof. Preferred metal salts include iron (II) and (III)salts, copper (II) salts and manganese (II) salts. Preferred iron saltsare selected from the group consisting of ferrous sulfate, ferricsulfate, ferrous perchlorate, ferric perchlorate, ferrous nitrate andferric nitrate.

[0027] Preferred iron oxyhydroxides include goethite, hematite andmagnetite. Iron chelates include, for example, Fe(II/III)-EDTA,Fe(II/III)-NTA, Fe(II/III-hydroxyethyliminodiacetic acid (HEIDA),Fe(II/III)-mucic acid, Fe(II/III)-malonic acid, Fe(II/III)-ketomalonicacid, Fe(II/III)-DL-tartaric acid, Fe(II/III)-citric acid,Fe(II/III)-oxalic acid, Fe(II/III)-gallic acid, Fe(II/III)-picolinicacid, Fe(II/III)-dipicolinic acid, Fe(II/III)-catechol,Fe(II/III)-1,2-dihydroxybenzoic acid, Fe(II/III)-quercertin,Fe(II/III)-pyrocatechol violet, Fe(II/III-alizarin red,Fe(II/III)-rhodizonic acid, Fe(II/III)-tetrahydroxy-1,4-quinone,Fe(II/III)-ascorbic acid, and Fe(II/III)-hexaketocyclohexane (HKCH). Themost preferred catalyst is iron sulfate or Fe(II/III) EDTA.

[0028] pH modifying agents include strong bases such as alkali metalhydroxides (e.g. sodium hydroxide) and weak bases such as salts of weakacids (e.g. sodium acetate and sodium carbonate).

[0029] The in situ environment for most soil and/or groundwater sitesincludes a water table which is the uppermost level of the below-ground,geological formation that is saturated with water. Water pressure in thepores of the soil or rock is equal to atmospheric pressure. Above thewater table is the unsaturated zone or vadose region comprising theupper layers of soil in which pore spaces or rock are filled with air orwater at less than atmospheric pressure. The capillary fringe is thatportion of the vadose region which lies just above the water table.

[0030] The capillary fringe is formed by contact between the water tableand the dry porous material constituting the vadose region. The waterfrom the water table rises into the dry porous material due to surfacetension because of an unbalanced molecular attraction of the water atthe boundary, thus forming the capillary fringe. The capillary fringehouses the majority of the light non-aqueous phase liquid contamination(LNAPLs) having a density less than water (e.g. BTEX contamination) dueto the LNAPLs tendency to remain on the surface of the water table.Seasonal changes in water table elevation may deposit additionalcontamination in the capillary fringe and/or recontaminate the watertable with contamination from the capillary fringe.

[0031] The source of the oxidizing agent and the substantially pHneutralized catalytic reagent can be administered to the in situenvironment by any method considered conventional in the art. Forexample, administration can be directly into the groundwater through ahorizontal or vertical well or into subterranean soil through a well orinfiltration trenches at or near the site of contamination. In apreferred form of the present invention, the capillary fringeconstitutes the in situ environment for treatment of the majority ofcontaminants that are less dense than water. The stabilized source ofthe oxidizing agent and catalytic reagent are administered into thecapillary fringe of the contaminated site through wells or trenches andthe like.

[0032] Contamination that is denser than water (i.e. Dense non aqueousphase liquids or DNAPLs) mostly resides at or near the bottom of thesaturated zone due to its tendency to sink in water (e.g. chlorinatedsolvents). In a preferred form of the present invention, the saturatedzone constitutes the in situ environment for treatment of the majorityof contaminants that are denser than water. The stabilized source of theoxidizing agent and catalytic reagent are administered into the bottomlayers of the saturated zone through wells or trenches and the like.

[0033] The saturation depth or depth of the saturated zone is very highat some contaminated sites (greater than 20-50 feet). Treatment ofcontamination in the saturated zone at such sites is achieved by varyingthe depth at which the stabilized source of the oxidizing agent andcatalytic reagent are administered. Typically, injection wells withadjustable depth injectors are utilized at sites with high saturationdepth. In a preferred form of the invention, the depth variation isperformed after each treatment cycle in increments varying from 5-10feet.

[0034] As previously indicated, the reagents of the present inventioncan be administered under elevated pressures into hard to reach placessuch as fractures within underlying bedrock. These fractures arecollecting places for contaminants which are typically more dense thanwater. When administered the present reagents are able to penetrate thefractures, contact the contaminants and convert the same to harmlesscompounds.

[0035] Injection of the stabilized source of the oxidizing agent and thecatalytic reagent can be accomplished by installing steel lined wells oropen hole type wells into the bedrock. Packers and bladdersconventionally employed in downhole drilling can be employed to assistin isolating discrete fractures and accessing the contaminants with thereagents. The reagents are then injected into the fractures at appliedelevated pressures, typically in the range of from about 20 to 100 psi.

[0036] The administration of the present reagents into the in situenvironment including bedrock fractures under elevated pressures can beaccomplished either alone or in conjunction with conventional treatmentsystems. Such systems include pump and treat systems which pump thecontaminated groundwater out of the in situ environment and soil vaporextraction systems in which a vacuum is applied to the site ofcontamination to physically enhance volatilization and desorption of thecontaminants from soil and/or groundwater.

[0037] The use of the metal catalyst reagent as a promoter for theformation of the oxidizing agent is advantageous because the reagent canbe easily generated by readily available mixers which do not requireexcessive labor to operate. In addition, unlike conventional Fenton'ssystems which are highly dependent on pH and require aggressiveadjustment of site pH to acidic conditions, it has been found that thepresent system functions efficiently at substantially neutral pH ranges,consistent with native pH found in many subsurface environments.

[0038] As indicated above, the stabilized source of the oxidizing agentand the metal catalyst reagent can be administered directly into the insitu environment. In a preferred form of the invention, the amount ofthe reagents and the number of treatment cycles are predetermined. Forexample, samples of the contaminated soil and/or groundwater are takenand the concentrations of the respective reagents required for in situtreatment are then determined based on the amount of the reagents neededto at least substantially rid the samples of the contaminants containedtherein.

[0039] More specifically, a sample of the soil and/or groundwater isanalyzed to determine the concentration of the contaminants of interest(e.g. hydrocarbons). Analysis of volatile hydrocarbons can be made bygas chromatographic/mass spectrometric systems which follow, forexample, EPA Method 624 for aqueous samples and EPA Method 8260 for soilsamples. Semi-volatiles are analyzed in a similar manner according to,for example, EPA Method 625 for aqueous samples and EPA Method 8270 forsoil samples.

[0040] Results from these analyses are used to determine the reagentcombinations for treatment of the sample based on the type andconcentration of the contaminants. A specific molar ratio of thereagents is used for the sample based on prior research, comparativesamples and the like. Typical sample weights can be in the range of fromabout 120 to 150 grams.

[0041] Sample analysis is also employed to determine the number oftreatment cycles which may be necessary to achieve the desired reductionin the level of contaminants. While one treatment cycle may be used, itis often desirable to employ a plurality of treatment cycles dependingon the type and concentration of pollutants. The number of treatmentcycles is determined in part by monitoring the performance of thereagents, particularly the source of the oxidizing agent once injectedinto the soil and/or groundwater.

[0042] In operation, a catalyst such as a chelated iron (II) salt ispremixed with water and optionally, if necessary, titrated with a pHadjusting agent such as a base (e.g. sodium hydroxide) within a pH rangeof from about 5 to 8. The metal catalyst reagent comprised of thecatalyst, and the stabilized source of the oxidizing agent are injectedinto sealed vials with a syringe. The reagent doses are given asspecific treatment cycles with the expectation that the samples willtypically require as few as one treatment cycle and as many as fivetreatment cycles in order to substantially or completely convert thecontaminants to harmless by-products. Each additional treatment cycle isgiven after ensuring that greater than 75% of source of the oxidizingagent injected to that point has been consumed.

[0043] A control sample is set up for each type of sample undergoing thestudy to correct for any volatilization loss. All experimental vials areleft undisturbed overnight at room temperature. On the following day thesamples are analyzed to determine the concentration of contaminants bythe above-mentioned EPA procedure. Once the results are obtained, theymay be extrapolated to provide a suitable amount of the stabilizedsource of the oxidizing agent and metal catalyst reagent necessary totreat the contaminants in situ.

[0044] Injection of the stabilized source of the oxidizing agent andmetal catalyst reagent may be performed under both applied andhydrostatic pressure into the in situ environment. Flow rates will varydepending on the subsurface soil characteristics with faster ratesassociated with more highly permeable soils (e.g. gravel and/or sand).Slower rates as low as 0.01 gallons per minute may be used for lesspermeable soils (e.g. clays and/or silts). The stabilized source of theoxidizing agent and metal catalyst reagent may be injected into thesubsurface and allowed to disperse over a period of time necessary toachieve equalization such as about 24 hours. The equalization period mayvary depending, in part, on the soil type.

[0045] In less permeable soils, injection procedures are preferablyassociated with a pressurized system. A typical system involvesinjection wells installed with screens set at specific levels to allowfor higher pressures encountered by pumping into less permeable soils.The pumping system can include a low horsepower pump at pressuresranging from between about 10 and 40 lbs. per square inch. Thestabilized source of the oxidizing agent and catalytic reagent may bepumped in short pulse injections or in a long steady flow as desired. Inanother form of the invention, the injection efficiency into lesspermeable soils is improved by subjecting the less permeable areas tohydraulic fracturing or other techniques to create fissures within thesubsurface that render the in situ environment more permeable.

[0046] In a preferred form of the invention applicable for mostcontaminants that are less dense than water, the stabilized source ofthe oxidizing agent and metal catalyst reagent are injected directlyinto the capillary fringe, located just above the water table. This canbe accomplished in a conventional manner by installing a well screenedin the capillary fringe and injecting the reagents into the well screen.

[0047] In another preferred form of the invention applicable forcontaminants that are denser than water, the stabilized source of theoxidizing agent and the catalytic reagent are administered into thelower layer of the saturated zone. This can be accomplished byinstalling a well screened through the bottom portion of the saturatedzone and extending the associated injectors to the bottom of theaquifer.

[0048] As previously indicated, the stabilized source of the oxidizingagent and the catalytic reagent are alternately injected (i.e. incycles) into the in situ environment. In another embodiment, thestabilized source of the oxidizing agent and the catalytic reagent arecontinuously injected into the in situ environment.

[0049] In particular, the effects of naturally occurring mineralsincluding their reactivity with the peroxide and metal catalyst can havea dramatic effect on the extent of the formation of the oxidizing agent.Typically, it has been found that continuous injection of stabilizedsource of oxidizer and the catalytic reagent into in situ environmentwith low to moderate permeability and cycled injection into in situenvironment with moderate to high permeability allows for improvedefficiency of conversion of reactive species throughout the plume in thesubsurface.

What is claimed is:
 1. A reagent for use in the treatment ofcontaminants in an in situ environment, comprising: an aqueous solutioncomprising an effective amount of a metal catalyst selected from atleast one member of the group consisting of Fe (II) salts, Fe (III)salts, Fe (II) chelates, Fe (III) chelates and combinations thereof; andan optional pH modifying agent in an amount sufficient to provide a pHfor said reagent in the range of from about 5 to
 8. 2. The reagent ofclaim 1 wherein the pH modifying agent is selected from water and abase.3. The reagent of claim 1 wherein said metal catalyst is Fe (II) or Fe(III) sulfate.
 4. The reagent of claim 1 wherein the metal catalyst isFe (II) or (III) EDTA chelate.
 5. The reagent of claim 2 wherein the pHmodifying agent is water.
 6. The reagent of claim 2 wherein the pHmodifying agent is sodium hydroxide.
 7. A method of treatingcontaminants in an in situ environment, comprising: preparing an aqueoussolution comprising an effective amount of a metal catalyst selectedfrom at least one member of the group consisting of Fe (II) salts, Fe(III) salts, Fe (II) chelates, Fe (III) chelates and combinationsthereof; optionally adding a pH modifying agent to said aqueous solutionin an amount sufficient to provide a pH for said reagent in the range offrom about 5 to 8; adding a source of an oxidizing agent to said in situenvironment in an amount sufficient to treat said contaminants; andadding said aqueous catalyst solution to said in situ environment in thepresence of said source of the oxidizing agent in an amount sufficientto promote the formation of the oxidizing agent in an amount sufficientto treat said contaminants.
 8. The method of claim 7 wherein said sourceof the oxidizing agent is a peroxide.
 9. The method of claim 7 whereinthe pH modifying agent is selected from water and a base.
 10. The methodof claim 8 wherein the source of the peroxide is selected from the groupconsisting hydrogen peroxide, sodium peroxide and calcium peroxide. 11.The method of claim 10 wherein the source of the peroxide is hydrogenperoxide.
 12. The method of claim 7 further comprising stabilizing saidsource of the oxidizing agent.
 13. The method of claim 12 comprisingstabilizing the source of the peroxide with a stabilizer selected fromthe group consisting of acids, salts, and mixtures thereof.
 14. Themethod of claim 13 wherein the stabilizer is selected from the groupconsisting of phosphoric acid, monopotassium phosphate and combinationsthereof.
 15. The method of claim 7 comprising alternately adding thesource of the oxidizing agent and the aqueous catalyst solution to thein situ environment.
 16. The method of claim 7 comprising continuouslyadding the oxidizing agent and the aqueous catalyst solution to the insitu environment.
 17. The method of claim 15 wherein the aqueouscatalyst solution is first added to the in situ followed by source ofthe oxidizing agent.
 18. The method of claim 15 wherein source of theoxidizing agent is first added followed by said aqueous catalystsolution.
 19. The method of claim 16 wherein the aqueous catalystsolution is first added to the in situ environment followed by source ofthe oxidizing agent.
 20. The method of claim 16 wherein source of theoxidizing agent is first added to the in situ environment followed bysaid aqueous catalyst solution.
 21. The method of claim 1 wherein the insitu environment comprises at least one of soils and groundwater withmoderate to high permeability.
 22. The method of claim 1 wherein the insitu environment comprises at least one of soils and groundwater withlow to moderate permeability.
 23. The method of claim 7 wherein at leasta portion of the oxidizing agent comprises hydroxyl radicals.
 24. Themethod of claim 7 wherein the in situ environment is selected from thegroup consisting of soil, groundwater, and fractured bedrock.
 25. Themethod of claim 7 wherein the steps of adding the source of theoxidizing agent and the aqueous catalyst solution are made at anelevated pressure.
 26. The method of claim 25 wherein the elevatedpressure is from about 20 to 100 psi.
 27. The method of claim 25 whereinthe in situ environment is fractured bedrock.
 28. The method of claim 24comprising adding the source of the oxidizing agent and the aqueouscatalyst solution to a region within the in situ environment known asthe capillary fringe.
 29. The method of claim 28 wherein thecontaminants to be treated are less dense than water.
 30. The method ofclaim 24 comprising adding the source of the oxidizing agent and theaqueous catalyst solution to a region of the in situ environmentcomprising the lower layers of the saturated zone.
 31. The method ofclaim 30 wherein the contaminants are denser than water.
 32. The methodof claim 30 comprising adding the source of the oxidizing agent and theaqueous catalyst solution to the lower layers of the saturated zone atdifferent depths when the depth of the lower layer of the saturated zoneis greater than 20 feet.
 33. The method of claim 32 further comprisingadding multiple doses of the source of the oxidizing agent and theaqueous catalyst solution.
 34. The method of claim 32 wherein thedifference in depth of each dose is in the range of from about 5-10feet.
 35. The method of claim 7 wherein the source of oxidizing agent isperoxide in water at concentration of up to 35% by weight.
 36. Themethod of claim 35 wherein the preferred concentration of the source ofthe oxidizing agent is less than 10%.